Gotei 13

The Gotei 13 (護廷十三隊, goteijūsantai, 13 Division Imperial Guards, or 13 Court Guard Squads in the English dubbed version?) is the organization which most shinigami join. It is split into thirteen divisions (hence the name), with several divisions having certain specializations. The 4th Division is the medical/supply division, the 11th Division is the combat division (specialization in swordsmanship), and the 12th Division is the research/scientific division. The 9th Division was shown, in a Shinigami Cup extra, to be in charge of newspaper and magazine-related duties. It's unclear if the other divisions are specialized, as the four above are the only ones who receive any significant attention apart from their members.